The semiconductor integrated circuit (IC) industry has experienced exponential growth. Technological advances in IC materials and design have produced generations of ICs where each generation has smaller and more complex circuits than the previous generation. In the course of IC evolution, functional density (i.e., the number of interconnected devices per chip area) has generally increased while geometry size (i.e., the smallest component (or line) that can be created using a fabrication process) has decreased. This scaling down process generally provides benefits by increasing production efficiency and lowering associated costs. Such scaling down has also increased the complexity of processing and manufacturing ICs.
For example, as semiconductor devices, such as metal-oxide-semiconductor field effect transistors (MOSFETs), are scaled down through various technology nodes, strained source/drain (S/D) features have been implemented to enhance carrier mobility and improve device performance. One approach of forming a MOSFET with strained S/D features grows epitaxial silicon (Si) to form raised S/D features for an n-type device, and grows epitaxial silicon germanium (SiGe) to form raised S/D features for a p-type device. Various techniques directed at shapes, configurations, and materials of these S/D features have been implemented to further improve transistor device performance. Although existing approaches have been generally adequate for their intended purposes, they have not been entirely satisfactory in all respects.